<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <script src="../js/vue@2.7.16.js"></script>
    <title>监视属性</title>
</head>

<body>
    <div id="app">
        <h2>天气很什么：{{isHot}}</h2>
        <button @click="changeWeather">切换天气</button>
    </div>
</body>

<script>
    const vm = new Vue({
        el: "#app",
        data: {
            isHot: true
        },
        methods: {
            changeWeather() {
                this.isHot = !this.isHot
            }
        },
        watch: {
            immediate: true,
            isHot: {
                handler(newVal, oldVal) {
                    console.log("值修改", newVal, oldVal);
                }
            }
        }
    })
</script>

</html>